Areas of Research

Graduate Program Affiliations

Figure 1: TRAJECTORY EVENTS (a) We recorded simultaneous spiking activity from up to 250 hippocampal neurons in multiple sessions in rats (N=4) performing a spatial memory task in an open arena, using 40-tetrode drives targeted bilaterally to hippocampal CA1. During brief pauses in running, whole populations spike together, as indicated by red line. (b) Each frame shows
the representation of position, which is tightly focused in a single location. Across frames, the represented position moves smoothly across the arena. The rat was stationary throughout the event. (c) Eight examples: successive frames are collapsed to represent the full event. Trajectory events consistently started at the current location and ended at the remembered goal, and depicted the precise path immediately taken. Cyan arrowhead: rat position, head direction. Cyan circle: goal. Cyan line: trajectory of peak position probability. Number: event duration (ms). Adapted from Pfeiffer and Foster (2013).

Neural Ensemble Mechanisms of Learning and Memory

Research in the Foster laboratory focuses on how large populations (or “ensembles”) of neurons encode and process information in awake, behaving animals. We use high density tetrode recording techniques to investigate the activity of neural ensembles during tasks which incorporate a variety of learning, memory, inference, planning and decision making demands.

Currently we are interested in how hippocampal ensembles in rodents process navigationally relevant information. We have found that precise sequences of neurons are activated repeatedly during behavior, reflecting memory for immediately preceding spatial experience.

We are seeking to determine: (a) the cellular and molecular basis of this sequential activation, and how it relates to synaptic plasticity mechanisms; (b) the functional capabilities of sequential activation, particularly in terms of inferring and planning navigationally relevant trajectories; and (c) the functional relevance of hippocampal sequential activation in guiding behavior, particularly in terms of how the hippocampus interfaces with brain regions involved in reward learning and reward-based decision making.

Our work has potential clinical relevance for the many disorders that severely affect the hippocampus, including Alzheimer’s disease and epilepsy, and those disorders that affect interfacing brain regions in the basal ganglia, such as Parkinson’s disease and Huntington’s disease, and for complex disorders such as schizophrenia which we study directly through the use of animal models.